After a vigorous debate Thursday, the board of the Metropolitan Transportation Authority temporarily suspended the monthly fee that Los Angeles County residents pay on devices required to use new toll lanes.

Metro's board of directors voted 7 to 4 to waive the $3 charge for six months.

The motion, proposed by county Supervisor Zev Yaroslavsky, addresses a complaint raised by motorists who bought $40 FasTrak transponders but don't regularly use the toll lanes on the 110 and 10 freeways. Drivers must use the lanes four times a month to avoid the fee.

The transponders track toll lane usage, which can cost several dollars per day for round-trip drivers traveling alone.

"The infrequent users who live in Los Angeles are really being treated unfairly," Yaroslavsky told the board, adding he's received dozens of letters protesting the monthly fee.

Many solo drivers or carpoolers who would use the toll lanes have not bought transponders because of the monthly fee, project director Stephanie Wiggins told the board.

During the six months that the fee is waived, Metro will assess the effect on the project's revenue and the number of users.